Diffraction studies of WS₂ crystallographic ordering during laser MBE growth on Al₂O₃(0001)

Abstract

For optimal integration of 2D materials into fab-compatible processes, it is essential to grow them directly onto suitable insulating substrates, thereby avoiding error-prone transfer procedures. In the present paper, ultrathin films of WS₂ were grown on Al₂O₃ using laser molecular beam epitaxy (LMBE). By applying our advanced 3D reciprocal space mapping technique, the presence of long-range order in the growing layers during the growth process could be identified. We observed a strong influence of pre-growth annealing of the substrate on the lateral crystallographic lattice ordering of ultrathin WS₂ films. In particular, it was found that high-temperature annealing of the substrate before film growth changed the preferential lattice orientation of WS₂ crystallites from 30° to 0° with respect to Al₂O₃. These observations contribute to a better understanding of epitaxial growth processes and crystallographic relationships between WS₂ and Al₂O₃. We demonstrate growth of the WS₂ film on the Al₂O₃ substrate by using the LMBE method at significantly lower substrate temperatures (500 °C) than that used by other techniques. The feasibility of achieving better structural order in WS₂ films through optimized substrate treatments using LMBE presents significant implications for the future integration of 2D materials in electronic devices.